def get_breadcrumb(cat3):    """根据三级类型来构造面包屑导航数据"""    cat1 = cat3.parent.parent    cat1.url = cat1.goodschannel_set.all()[0].url    breadcrumb = {        'cat1': cat1,        'cat2': cat3.parent,        'cat3': cat3    }    return breadcrumb